Book Image

Learn Linux Shell Scripting – Fundamentals of Bash 4.4

By : Sebastiaan Tammer
Book Image

Learn Linux Shell Scripting – Fundamentals of Bash 4.4

By: Sebastiaan Tammer

Overview of this book

Shell scripts allow us to program commands in chains and have the system execute them as a scripted event, just like batch files. This book will start with an overview of Linux and Bash shell scripting, and then quickly deep dive into helping you set up your local environment, before introducing you to tools that are used to write shell scripts. The next set of chapters will focus on helping you understand Linux under the hood and what Bash provides the user. Soon, you will have embarked on your journey along the command line. You will now begin writing actual scripts instead of commands, and will be introduced to practical applications for scripts. The final set of chapters will deep dive into the more advanced topics in shell scripting. These advanced topics will take you from simple scripts to reusable, valuable programs that exist in the real world. The final chapter will leave you with some handy tips and tricks and, as regards the most frequently used commands, a cheat sheet containing the most interesting flags and options will also be provided. After completing this book, you should feel confident about starting your own shell scripting projects, no matter how simple or complex the task previously seemed. We aim to teach you how to script and what to consider, to complement the clear-cut patterns that you can use in your daily scripting challenges.
Table of Contents (24 chapters)
Title Page
About Packt
Contributors
Preface
Free Chapter
1
Introduction
Index

Variable manipulation


Parameter expansion in Bash deals with more than just default values, input checking, and parameter length. It actually also allows us to manipulate the variables before we use them. In this second part of this chapter, we'll explore the capabilities within parameter expansion that deal with variable manipulation (our terminology; as far as Bash is concerned, these are just normal parameter expansions).

We'll kick this off with pattern substitution, something you should be familiar with after our explanation of sed in Chapter 10, Regular Expressions.

Pattern substitution

Simply said, pattern substitution allows us to substitute a pattern with something else (who would have thought!). This is what we could already do with sed:

reader@ubuntu:~/scripts/chapter_16$ echo "Hi"
Hi
reader@ubuntu:~/scripts/chapter_16$ echo "Hi" | sed 's/Hi/Bye/'
Bye

Initially, our echo contains the word Hi. We then pipe it through sed, in which we look for the patternHi, which we will substitute...